A need exists for improved methods for thickening, e.g., gelling, hydrophobic liquids. There are several reasons for the need for such methods.
Over the last twenty years, for example, the world has witnessed several marine oil spills releasing millions of gallons of oil into the ocean—the most notable being the 1989 Exxon Valdez incident that took place in Alaska, and more recently the explosion of a BP oil well, and resulting oil spill, in the Gulf of Mexico. Such haphazard oil spreads cause tremendous damage to the ecological system. The scale of such disasters has drawn attention to the need for new materials to contain oil spills and reclaim the oil. Many types of materials have been devised for oil spill control and cleanup, and several of these materials have been commercialized. However, problems exist with each of these current technologies.
Molecular gelators (MGs) are an alternate class of materials that may be used as solidifiers of oil. These are typically organic molecules of low molecular-weight that self-assemble into filaments or fibers in a variety of liquids. Despite the potential benefits, MGs are not currently used for oil spill treatment for various reasons. For example, many MGs are complex organic moieties that are potentially harmful to the environment. Furthermore, MGs are often specialized molecules that are synthesized by complex, multi-step procedures—in turn, it is doubtful whether the materials can be delivered at low cost and in large quantities that are required for a major oil spill. Also, the action of MGs requires their dissolution in the solvent, which is usually accomplished by heating a mixture of the MG powder and solvent up to a high temperature. This is impractical for oil spill treatment where it is imperative to be able to induce gelation of the oil under ambient conditions.
It is advantageous for the MG to be capable of phase-selective gelation (PSG), i.e., the MG should preferentially gel the oil layer even when it is in contact with the water. In other words, water should not impair the oil-gelling properties of the MG. This advantage can be challenging because many MGs are amphiphilic molecules, i.e., they have water-loving and water-hating parts, and this is a key to their gelling ability. When contacted with water, these molecules partition to the oil-water interface (thereby acting as surfactants or emulsifiers)—as a result, their gelling ability is affected. Due to the above challenges, only a few PSGs of the oil phase from an oil-water mixture have been reported. However, existing PSGs are complex molecules, they require heat to be dissolved in the solvent, and their environmental suitability is questionable—thus, the practical use of these PSGs for oil spill treatment is limited. There is a need for new and improved PSGs that can avoid the above problems.
Another application of methods for thickening hydrophobic liquids is in structuring vegetable oils. Currently, the most common methods use hypercholesterolemic fatty acids, such as stearic acid, as structuring agents. For edible oils, however, healthier methods are desirable.
There is also the need for gel-based formulations to enhance the delivery of drugs and increase the bioavailability of drugs at targeted regions of the body.
MGs may also be used in making oil in water microemulsions. The microemulsions may then be used to solubilize or encapsulate hydrophilic and hydrophobic molecules.
Another application of PSGs might be to covert fuel or crude oil fractions to solid-like material to facilitate the transportation of the fuels and prevent the spreading of liquids in the event of accidental or intentional fuel spills.